1. Field of the Invention
The present invention relates to a method of producing a glass preform and an optical fiber.
2. Description of the Related Art
Conventionally, reduction in transmission loss is required for a long haul transmission fiber. To address this, in recent years, a method of restraining Rayleigh scattering by using a pure silica core has been studied. K. Nagayama et Al., Electron. Lett., 38, PP. 1168-1169 (2002) (hereinafter to be referred to as Non-Patent Literature 1) proposes a structure in which a light is guided by decreasing a refractive index of a cladding layer by disposing the cladding layer doped with fluorine around a pure silica core. Japanese Patent No. 3270148 (hereinafter to be referred to as Patent Literature 1) describes a structure in which a core portion of an optical fiber is doped with an alkali metal and a cladding portion is doped with fluorine.